The Senate could amend the measure and pass it, then send it back to the House for approval, and then -- if the House approves -- on to President Obama's desk. In amending the measure, Senate Democrats could change scope of spending cuts and the duration of the debt-ceiling increase (from a short-term one to a longer-term one), among other options.

The Senate could take up the Boehner plan again unchanged, and if it passed, send it to Obama's desk for his signature (or veto). But Democrats have vowed that no aspect of the Boehner plan will see the light of day.

The Senate could take up Reid's debt-ceiling plan. If it passed, it would head over to the House.

The Senate could fail to pass any measure -- be it the unchanged Boehner plan, an amended Boehner plan or the Reid plan. At that point, congressional leaders and the White House would likely have to scramble to craft an eleventh-hour deal to avoid default or else, well, the nation would default on its debt obligations.